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T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONE SYSTEM 5 Sheets-Sheet 1original Filed March 21, 1908 TsZbuZ G. Marfm.

April 13 1926.

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April 9 T. c5. MARTIN TWOJIIRE AUTOMATIC TELEPHONE SYSTEM 5 h 0 t m H HT, a P m M 5 W yd? o i i Filed March 21, 1908 April 13,1926. R 16,317

T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONE SYSTEM Qriginal Filed March 211908 5 Sheets-Sheet 4 R 16,317 T. G. MARTIN TWO-WIRE AUTOMATIC TELEPHONESYSTEM m 9 1 3 m A original Filed March 21, 1908 v 5 Sheets-Sheet 5Inusn 1211- Talbul 52H STA Reissued Apr. 13, 1926.

"res PATENrO FFICE.

.mmo'r c mm, or omcaeo, rumors, ASSIGNOR, BY MESNE assremn'rsso 'nm, orcmcaeo, rumors, A conrona'rxon or 1mm;-

- TWO-m AUTOMATIO'TELE PHONE-SYSTBM.

application fled mm, 1908, saw no.

en ine In. 1,249,159, dated December 4, 1m. -10. 5'

* To allnohom in may come-m:

- Bent knownthat I, TALno'r G. MARTIN, a citizen of the United States ofAmerica, and resident of Chicago, Cook County, Illinois, .have inventeda (ertain new and useful Improvement in Two-Wire Automatic Tele phoneSystems, of which the following is a specification. My invention relatesto telephone systems in general; but more particularly to automatic orsemi-automatic telephone exchange system, and especially to systems inwhich the. subscribers" lines are free from operatgroimds outside oftheexchgn e or central Station, these rbeilig'ordinari y known astwo-wiresystems. P' Y Objects of my invention are to provide a two-wim system--in which automatic. partyline service can be given the subscribersthereof; to provide a two-wire automatic telephone exchange system inwhich subscriberson the same line signal each other by means ofush-buttons at their respective stations, whil a called subscriber onanother line is signaled automatically from the exchange or centralstation; to provide a twowire automatie telephone exchange system inwhich the connectors ,willlock .on busy called lines, without closingthe calling line in connection r therewith, the calling subscriber beingat the same time given a bus) signal; to provide atwo-wire automatictelophone exchange system in which provision is made for enabling aparty-line subscriber to call back on his own line, in order toestablishtelephonic communication with another'subscriber on the same line; anda.

.provide certain novel details and-features of improvement andcombinations tending to increase the general etficiency andserviceability of a-:telephone exchange system of Y this particularcharacter.

To the foregoing and other useful endsv my invention consists in mattershereinafter set forth and claimed.

In the accompanying drawings, Figure 1 is a diagrammatic representationof-party- "line equipment embodying the principles of my invention. Thesubstations A and A are allotted to a common line which terminates atthecentral office in the line switch Renewed April 12, 1e17, Serial No.161.050.

Application for reissue filed August 30,1918. Serial C. At D isrepresented the master switch for controlling the line switches of thegroup of. which the switch C is ,a member. represents diagrammatically afirst-selector switch. v Fig. 2 represents diagrammatically the centraloffice second-selector switch F and the connector switch H. At C isshown a line switch allotted to the party-line of which substations Aand A are members. A central battery B having its positive terminalpreferably grounded at G provides battery current for talking andoperating purposes, Fig. 3 shows how a subscriber may-operate centralofiice switches to call back and signal a subscriber on his own line.

Fig. 4 represents more fully the I line switch C and the controllingmaster switch D. Fig. 5 is a detail View of the master switch bank 0.

rangement of the lines by means of which the different substations maybe signaled selectively.

In this system each subscribers line is, of course, provided with a lineswitch similar to the line switch C, and usually one- .hundred of these,form a group. Also, to each Such group there is allotted a group offirst-selector switches in common. The firstselector switches may'inturn be operated to first select any one of a number'of groups ofsecond-selectors, and then some one, of the selected group which may beidle. The second-selector switches may in turn be operated to firstselect any one of a number of groups of connector switches, and thensome one of the connectors of the selected group which may be idle. Eachgroup of connector-switches is also arranged to take care of one-hundredsubscribersthat is, if any subscriber in the system wants to callanother subscriber he must, through the ,medium of the first selectorand second-selector switches, pick out a certain group of connectors,any one of the connectors of-which group is capableof establishing thefinal connection with the desired subscriber in a particular, hundred.

or approved type. As shown, it will be seen that substation A issomewhat different from e .usual lutomatio substation, mid subst on Abeing arranged and modified to operate in connection with a two-wirestas -that -With a s stem in which no gqmd is us at the subscriberssubstation. Substation A, for example, comprises the usual receiver 2,switch-hook 3, induction. coil 4 which consists of the griuniry'winding5 and secondary windin ti an'smitter 7, condenser 8, ringer 9 an im ulsewheel 10 which has the usual im- 16 which, when the switch-hook is up,peroiuding the transmitter mite the springs 17 and 18 to engage, therebybridging across the subscribers line conductors 19 and 20. the rimarycircuit inin series with the 'rimary winding 5; but when the switchhookis lowered the spring 17 is carried out of engagement with the spring 18and into engagement with the spring 18, whereby the ringer 9 in serieswith the condenser 8 is bridged across the line conductors 19 and 20instead. Furthermore, the substation A is provided with a .signalingbutton 5 which, when pressed, disengages the springs 6 and 7, wherebythe short-circuit or shunt around the resistance coil 8 is removed. Theline switch C (Fig. 4) comprises a plunger 21, plunger arm 22, tripmagnet 23, and switch-release magnet 24, all of which are assembled u ona suitable 'base or frame (not shown). he said switch-release ma net isrovided with an'armature 25 that 1s 'vot on a in 26 which rises from these of the swltch. The said armature cararmature 27 that is controlled bythe trip magnet 23. The pin 28 about which the armature 27'moves iscarried on the end of thearmature 25. The plunger 21 is pivotallysecured by'the pin 29 to the plunger arm 22, which latter is in. turnpivoted by a pin 30 that rises from the switch frame not shown). The lug31 may be stamped m the frame and is provided as a stop for the armature25. Upon the armature '27 is secured the member 32 which is adapted tonormally engage the end 33 of the plun 1 arm 22. Furthermore, the saidline switc is provided with a bank of terminals, usually ten in number,but only one of which is shown at Q (Fi 4). The said terminal Q is shownturned rom its true position with respect to the swing of the plunger21, and

the bushing 34 is correspondingly turned,

all for the pur ose of making the illustration clearer. T e terminal Q,comprises the springs 35 and 36, 37 and38, 39 and 40, and 41 and 42.These s rin are normally disconnected from eac ot er, but are driveninto contact, as shown in the drawings, when the plunger 21 engages thebank terminal Q. When the plunger 21 dise ages from the bank terminal Q,the said p unger may take one of two positions relative to the plungershaft 43-'-that is, the plunger may return to either locked or slidingengagement with the shaft 43. When the plunger 21 is in lockedengagement with the plunger shaft 43, the notch 44 is in engagement withthe flange or web 45 of the shaft 43; and when in sliding engagement thefan-like tail-piece 46 rests in the position shown by the dotted linesin Fig. 4--that is, when the plunger shaft is operated the plunger 21 isnot carried along with the locked plungers, but remains in the dottedposition, the plunger shaft sliding upon the edge of the tail-piece 46.The general operation of the switch is as follows: The trip magnet'23 isenergized when the receiver is removed from the switch-hook and thearmature 27 is attracted against the magnet cores. When the armature 27is attracted the catch 32 slides out of contact with the end 33 of theplunger arm 22, and the said plunger arm 22, owing to the tension of thespring 47, moves about the pin 30 and thrusts the plunger 21 into thebank terminal Q; and when the trip magnet again deen'ergizes, the triparmature 27 falls against the end 33 of the plunger arm 22, as shown.Furthermore, when the line switch operates, and the plunger 21 is thrustonto the bank terminal Q, the shaft 43 is advanced one step, as will beexplained, to carry the locked plungers opposite the next idletrunk-line. The switch is restored by the release magnet 24, on whoseenergization the armature 25 is attracted, and accordingly thetriparmature 27 is moved upwar-dly until the catch 32 slides overv theend 33; then whenthe release magnet 24 becomes deenergized the armature25 returns to normal position and remains at rest against the stop 31.Furthermore, since the ill] Ion

plunger arm 22 is now in engagement with the catch 32 of the armature27, the said plunger arm'is also moved about the pin 30, whereby theplunger 21 is moved from 'svidedfor controlling the sta isca in plunged.rnad But if after the plunger is released,

netjn engement. with the lunger shaft web'45. fter all the trunk-liiieshave been successively seized, the shaft 43 then passes from its lastposition and moves toward point, picking up the plunger 21 when twebiofthe said shaft over which the slot :44 normally rides arrives atthe position in which the plunger 21 was originally released-that is,the plunger passes into locked engagement with the shaft when the'slot44 slips over the web of said shaft.

From thence on the plunger 21 is carried in locked engagement by theshaft 43 until it in when another call is and before theshaft 43 returnsto pick up said plunger, the switch C is again operated, the plunger 21again engages the same terminal Q. The bridge-cut-ofi relay 48 isprosprings 49, 50,

-51 and 52, and, upon energizing, operates to shift the s rings 49 and51 out of engagement with tli thexsprings are thus operated the lineswitch Ci a disconnected from the substation line a springs 50 and 52.When conductors.

' Theimaster' switch D, which may be of any. suitable or approved type,is provided for operating the plunger shaft 43 and for controllingcertain circuits that will be dis ,olosed hereinafter. It, comprises thefollowing details: A motor magnet 53 for operatthe ratchet wheel 54,which latter is .designed for operating the plunger shaft 43 vthroughthe medium of the cam 55, and a differential rela 56- for controllingthe energizing circuit the motor ma et 53. The

., wiper,

said master switch also has a ank 0 com- .prlsing a plurality ofindividual contact segments a and a common metallic segment .57, asshown in Fig. 4. The wiper 58 is adalpted toremain in constantengagement wit thefiaank O, and to at all times, except when the wiperis passing from the extreme ,left t contact 59 to the extreme rightcontact 60, maintain some. one of thesegments a in electrical connectionwith, the common segment 57. As shown in Fig. the individual segments aare separated from the common segment 57 by the insulating strip61. The

spring 62 is provided so that when the wiper is carried to the contacton the extreme right, theupper part of the wiper 58 slides I on uidespring 62, thus preventing the From placing any of the individualsegments a in contact with the common segment 57, whereby someinterference might be caused with the master switch. The

wiper 58 is operated in a step-by-step manner by the ratchet wheel 54,through the medium of the cam member 55 rigidly secured torthe saidwiper 58, and is adapted to successively engage the pins 63, 64, 65

and 66 upon the said ratchet wheel 54; The

motor magnet 53 is provided with an armature 67 upon the end of whichthere is suitably secured apawl 68. Each time that the, said magnet is'energized, the armature 67 is attracted against the magnet cores, andthe pawl 68 engages a tooth on the ratchet wheel 54 thereby advancingthe latter one step. It will be seen, therefore, that. as the ratchetwheel 54 advances, the wiper58 advances step by step from right to left;and when the pin 63, for instance, clears the cam 55, the retractingspring 69 then re-- stores the wiper 58 to its first position at theright of the bank. and in engagement with the first segment 60. The saidmotor' magnet is provided with 'a couple of interrupter springs 70 and71 that are included in the energizing circuit of the said motor magnet,which energizing circuit also comprises the springs 72 and 73 controlledby the difl'erential relay 56. Therefore, whenever the difierentialrelay is energized the springs 72 and 73 are pressed into contact, andthe motor magnet 53"operates step by step as long as the differentialrelay 56 remains energized. Furthermore, it is assumed that the terminalQ of the line switch .C is the first terminal ofthe line switch bank.While in normal locking engagement with the shaft 43, the plunger 21 isretained in vfront of said terminal by the plunger shaft 43, wheneverthe master switch wiper 58 is in engagement with the bank segment 60;but as the motor magnet 53 advances the wiper 58 onto the second segment74, the said plunger and all idle plungers similarly engaging theshaft-43 ale carried opposite the next terminal of the line switch bank.It should be-noted that in each line switch bank all of the springs 35are permanently connected and may be made of one common piece. 'Thesprings 36, however, are individualthat is, there is one separate anddistinct spring for every bank set Q,,there bein ten in'the bank. Thesprin 37, 39 and are a 1 common, and the sprin 38, 40 and 42, like thesprings 36, are individual. For every bank terminal Q there is atrunk-line of three conductors 75, 76 and 77 leading to a selector; andthere is also a normal trunkline comprising the conductors 78, 79 and 80leadin to the connector banks. The subscribers 1ne conductors 19 and 20terminate in the springs 35 and 37 which, as has been stated, are commonsprings. When thesubscriber operates the line switch-C, and the plunger21 engages the terminal Q, the subscribers line conductors 19 and 20 areextended to the vertical and rotary trunk conductors 75 and 76, thencethrough the windings 21 and 22 of the relay 23,(as shown in Fig. 1) tothe first-selector switch E.

The first-selector switch shown atE is of the general type described inUnited States Letters Patent No. 815,321, granted March 41, like thesprings 35, a

vi nd abate the rotary trun-k line conductor trials the vertical ma 13,1906,,to Keith, Erickson & Erickson, and, CI, ,is modified to adapt itto operate in connection with a two-wire system. It embodies among otherdetails the following ieatnres: The switch shaft (not shown) car- ,riesthe negative and positive line wipers 81 and 82, and the private wiper83. The side :Ilitch is well known and comprises the side lswitch'wiqnrs 84, '85, 86 and 87 which may He i =1: ated as the vertical,rotary and private side switch wipers, and the rotary.magnetwviper,respectively. The side switch :ia-mnder the control of theprivate magnet 88, and when the side switch is in normal f m positionthe wipers 84, 85, 86 and 87 occupy thevcontact points 89, 90, 91 and92, nespectively. In the second position the -wipersnest on the contactpoints 93, 94, 95 a-l1d96, mespectively; and when in third po- 1 Editionthe contact points 97, 98, 99 and 100 mortgaged by their respectivewipers. The windings of the usual vertical and rotary dine relays are,in this case, combined into one double-wound relay 101 comprising the 2winding 102 which is connected with the blttery dead 103, and also withthe vertical "wank-line conductor, when the side switch wiper 84-h; infirst or second position. The second winding 104 is connected to ground,

7 'Whenthe side switch wiper'85 is in first or second sition. Throughthe medium of this don I -wound relay, and While the side switch is infirst position, the subscriber conet 105 which operates to raise theswitc shaft and wipers 81, 82 and 83 vertically. This line relay 101also controls the private magnet relay 106, which latter in turncontrols the private magnet 88. As usual, the private magnet controlsthe side switch. While the side switch in in second position the rotarymagnet 107 which operates to carrythe switch shaft and wipers "81,82-and 83 in a rotary direction, is ener- "4 6 The release magnet 108provides means for restoring the selector switch to normal position.Upon the switch shaft which carries the wipers 81, 82 and 83 there ismounted the arm 109 which, when the shaft is {raised one or more steps,permits the spring 110 to engage the contact point 111,

whereby the release magnet 108 is connected,

to the battery lead. Therelease relay 112 is provided for closing theenergizing circuit ofthe release magnet 108 after the switch isoperated. The'back-release relay 113 is provlded for opening theenergizing circuit through the release magnet 24 of the line switch. Therelays 106, 112 and 113 are slow-acting relaysthat is, they are soprovided with a copper shieldgthat when .enerd and the energizingcircuit then broken, fii e said relays remain in an operated posiftionfor a moment or so. In other words,

be recognized and understood.

they do not instantly return to normal position after the energizingcircuit is broken.

The second-selector F (Fig. 2) is similar to the first-selector E, andis provided with the usual double-wound line relay 114 having thewindings 115 and 116 connected with. the vertical and rotary side switchwipers 117 and 118 in the same manner in which the windings of the relay101 of the selector switch E are connected with their vertical androtary'side switch wipers. Since like parts are similarly represented,the rotary magnet 119 and the vertical magnet 120 will The releasemagnet 121 is operated in the same manner in connection with the switchF that the release :magnet 108 is operated in connection with the switchE. The private magnet 1 22 is controlled by the private magnetrelay'123. The release relay 124 of thesecond-selector switch F performsthe same function in connection with this switch-that the release relay112 and the back-release relay 113 perform in connection with thefirst-selector switch E-that is, the springs controlled by the relays112 and 113'are so arranged in the second-selector switch F that theyare controlled by the one relay 124. In the switch F the rela s 123 and124 are so arranged that they eenergize slowly,'the same as the relays106, 112 and 113 of the selector switch E.

The connector switch H is a modified form of the connector switchdisclosed in United States Letters Patent No. 815,176 granted March 13,1906, to Keith, Erickson Erickson. The connector switch shaft (notshown), like the switch shaft of the Belector, carries the line wipers125 and 126 and a private wiper 127. The connector switch is alsocontrolled by the calling subscriber though the medium of a doublewoundline relay 128. The line relay "128 is provided with the windings 129and 130. One terminal of the winding 129 is connected to the batterylead, while the other terminal is connected with the vertical trunklineconductor. The winding 130 is connect ed with ground and also with therotary trunk-line conductor. This line relay 128 directly controls thevertical magnet 131. The purpose of the vertical magnet 131 is to givethe shaft and shaft wipers a vertical motion, and the rotary magnet 132imparts to the shaft and shaft wipers a rotary or circular motion. Theconnector switch is also provided with the slow-acting release relay 133which is the same as'the release relay 124 of the second-selectorswitch. As usual, the private magnet relay 134 controls the privatemagnet 135, which latter controls the side switch wipers 136, 137, 138,139 and 140. The back hndge relay 141, comprising the windings 142 and143, provides the means whereby: the called subscriber. is furnishedwithhattery current for talking purposes. As here shown, my connector Iswitch. is of the automatic ringing typell thatis, a si aling of thecalled subscriber is nbb idepeliti ht upon the calling subscriberfissingia signaling button when he calls a not his own; for as-Soon ias.connection is'aestablished withthe desired line the interrupter 144intermittently closes an-energizing.v circuit through the ringer relay145,

whenehythe terminals of the ringer generator=.I-,are;intermittenlybridged across the normal conductors of. the called line. The relay 146visso arranged that if a busy line is called the connector. side switchis locked in second :Rosition, and the-calling subscriber is 'ren t ebusy-signal. The means whereby i with the winding 150 ofthe'induction-coil '30 151+; eThe windin 152 is connected with the 153,and w on the relay'146 energizes, fl8-:Wi%l,b6' explained, thebusy-signaling apparatus is connected with the connector or side switch136.

.tfi'heoperation of the system may be, more clearly understood from-anexplanation of m bpcrationi in establishing a connection. It will wbfiassumed that the subscriber at substation A wishes to call thesubscriber at substation A, to which latter is allottedthenumber 2220.To call the number 2220 (substation ,A, Fig. 2) the subscriber atsubstation A (Fig. 1) removes his receiver from the-switch-hook, andoperates the calls, ing dewice'for-eachdigit, in the well-knownmanner-that-is, when the receiver is removedrfromthe switch-hook apreliminary impulse provides an energizing circuit for the. m magnet 23of the line switch C, whereby the line switch C-is operated to an-Qidleand waiting or preselected trunk-lineleading to a first-selector switch.Tile-dill is turned for the first digit, and u n neturning to normalpositionoperates.

first-selector switch'to establish connection mith an idlertrunk-lineleading to a sepondvsele'ctor switch. in similar manner f the-dial, uponreturning to normal position gpgsthetsecond digigoperates the second- 1wr aswitch. Into. establish connection with an idle-truhk-liile .leading:to a con- 1m ,Lswiteh..-= she-amp delivered by iorthelast'two digits aredirected towardithe connector H, which latter opertgplace shaft wipersin connection with the contacts corresponding to the desired subscriber.The preliminary impulse for energizing the trip magnet 23 occurs whenthe receiver 2 is removed from the switch-hook 3 and the cam-arm I6permits the spring-.17 to engage the .spring 18., thereby removing thermger from across the line and bringing the primary circuit instead.When the primary circuit is thus' through battery Bto ground G. As soonas the .trip magnet 23 energizes, the armature 27 I is attracted and theplunger 21 is liberated and thrust into the bank terminal Qbythe spring47, assuming that the plunger .21 is opposite theterminal Q at the time.When the plunger 21 engages the bank terminal Q, an energizing clrcuitis established through the motor magnet relay 56, which inturn operatesto close an energizing circuit through the motor magnet 53 of themaster=switch D. The motor magnet then operates to advance all idleplungers that are in locking engagement with the shaft 43 opposite thenext idle bank terminal similar to the terminal Q. The circuit throughthe relay '56 extends from ground G through the winding 158 of therelay56 to the common segment 57, thence through the wiper 58, throughthe contact 60, conductor 159, bank terminal springs 42 and 41, throughthe Winding of therelease magnet 24 to the battery lead 103;, thencethrough battery B to ground G. Although this circuit includes therelease magnet 24, the said magnet does not operatively energize, sincethe winding of the relay 56 is of a high resistance, while the windingof the release magnet 24 is comparatively low. The relay 56, uponenergizing, operates to-place the sprlngs 72 and 73 n contact, whereby acircuit is completed throu h. the motor magnet 53, said circuit exteningsfrom ground G through the springs 72 and 73, motor magnet springsand 71, through the winding of the motor magnet 53 tothe battery lead103,. thence through batteryB to'ground G. The motor magnet 53, uponenergizing,'attracts its armature 67, whereby the pawl 68*engages theratchet wheel 54, advancing the latter one step. When the armature 67 isattractedagainst the magnet cores, the springs 70 and 71 disengage,thereby breaking the energizing circuit through the motor magnet 53 andpermitting the armature 67 to return to normll The cam 55, bein 1nengagemcn with the pin 63 upon the ratchet wheel 54gis operated toadvance the plunger shaft43 andall idle plungers that may be inmormallocked position with the shaft 43,

' opposite another terminal similar to the terminal Q, assuming the nextsucceeding trunk is idle.- Consequently, the wiper arm 58 1s carriedfrom the contact point 60 (which corresponds to the terminal Q) to thecontact point 74, which latter corresponds to the terminal beiore whichthe advanced idle plungers are now restin Suppose that nine subscribershave cal ed, and that the master switch has thus operated ninesteps,carrying the wiper 58 to. the last contact point 59. Now, when the motormagnet 53 operates for the next step, when the tenth subscriber calls,.the wipe:- 58 passes back and drops into engagement with the contactpointdO. If the first trunk is still busy thawiper58 finds a batterypotential on w the contact 60, and an energizing circuit is establishedthrough the differential relay 56,

which in turn operates "to close an energiz ing circuit through themotor magnet 53. The current through the said relay 56 fiows from =thesaid contact 60 through the wiper mm, however,

, time 58 to the common segment '57, and through the winding 158 of thedifl'erential relay: 56 to ground G. When this rela energizes itoperates to close the circuit -t rough the motor magnet 53, and themotor magnet then operates, as previously explained, to

rotate the ratchet wheel 54 one step, and the master switch bank wiper58 one step also andinto en gemont with the secondsegmerit 74. en thusadvanced one step the plunger shaft 43 carries all idle" plungers thatare in locking engagement with said shaft' 'op te the second bankterminal, as rcvious y explained. If there should still a 'arding'potential at the bank segment 7:, 'the differential relay 56 will remain energized, whereby the energizing circuit through the motor magnet53 is agam completed when the motor magnet sprlngs 70 and 72 againengage, and as a result the motor magnet 53 is again operated, wherebythe pin shaft 43 and the master switch wipor"5 are advanced anotherstep. This process continues as long as the wiper 58 con ti'nuesto findsegments with'guarding potentifls. As soon as an idle segment is the one"zing circuit throng; the relay 56 is bro n, at which I esaid may inturn breaks the energining circuit iorthe motor magnet 53, until thefloatsubscriber makes a. call. At the that the longer 21 enters the banktermini! Q the 0 lowing sptrings are pressed into'contnctr and 36, 3 and38, 39 and 40511111 4]. and 49. The an of the man rings 39 and 4t)closes a circuit through t e cut-oil relay 48 extending from ground Gthrough the springs 16 and 17, springs 18 and 19 of the relay 23 (whichis now energized, as will be explained), conductor 157, through thesprin s and 39, conductor 160, rel 48 to t c'battery lead 103, thencethrough li attery B to ground G. The said relay, upon energizing,operates to carry the springs 49 and51 out of en agement with thesprings and 52. on these springs disengage, the resistance coil 154 isdisconnected from the vertical line conductor 19, and the trip magnet 23is disconnected from the rotary line conductor 20. The engagement of thebank springs 39 and 40' also establishes a guarding potential by way ofthe normal conductor 8.0 to the connector private bank contactscorresponding to the line that terminates in the line switch C, torevent any subscriber from calling the sai line after the callingsubscriber at sub station A removes his receiver preparatory to making acall, as explained. Also, the closure of connection between the springs41 and 42 establishes a guarding potential at the master switch bankcontact 60, over the following circuit: irom battery B to the batterylead 103, thence throu h the winding of the release ma =et 24,'t rou hthe springs 41 and 42, con uctor 159 to t said contact point 60. It willbe understood that the bank terminal Q, being the first bank terminal ofthe line switch bank, corresponds to the first segment of the massterswitch bank 0 and, therefore, to the trunk-line the conductors 7 5, 76"and 77 of which terminate in the first-selector switch E. This ardingpotential protects the seized trun conductors 75, 76 and 77 from beingseized by other plungers, as already explained. The closure ofconnection between the springs 35 and 36 extends the calling subscribersvertical line conductor 19 to the vertical trunk conductor and the sideswitch wiper 84 of the first-selector switch E. The closure of contactbetween the springs 37 and 38 in a similar manner extends thesubscribers rotary line conductor 20 to the rotary trunk conductor 76and to the side switch wiper 85 of the selector E. The subscriber hasthus established connection with the next selector switch, which is nowoperated by the impulses that are delivered when the dial returns tonormal ositionfor the first digit. When the subscribers' line conductors19 and 20 are thus extended to the first-selector switch E, anenergizing circuit is established through the line relay 101 extendingfrom ground G 'through the winding 104 to'the contact point 90, sideswitch wiper 85, wind ing 22 of the rela 23, trunk conductor 76, throughthe ban springs 38 and 37 to the rotary line, conductor 20, throughthesprings 17fand 1*8, impulse springs and 14, rimary winding 5,transmitter 7 to the vertical line conductor 19, through the banksprings and 36, trunk conductor 7 5, windi ing 21 of the relay 23, sideswitch wiper 84,;con'tactpoint 89, through the winding 102 to thebattery lead'103, thence through battery B to, round G. Both windings'oftherelay 23 eing included in this circuit, 1 the said relay operativelyenergizes to place the springs 19 and 18 in contact, thereby providingthe guarding potential for pro- V tecting' the line and completing anenergizing circuit forthe-bridge-cut-off relay 48, as

is'established through the-releaserelay 112 i e iitending from ground Grthrough the circuit is established through the private magnet 88. Thiscircuit extends from ground G through the springs 167 and 168, privatemagnet 88 to the battery lead 103, thence through battery B to groundG'. The private magnet relay 106 deenergizes after the last verticalimpulse, since its energizing circuit is no longer maintained after'thesprings 161 and 166 disengage. Hence, the said relay I deenergizes,permitting the springs 167 and 168 to disengage, whereby the energizingcircuit through the private magnet 88 is in turn broken, which privatemagnet now deenergizes and permits the side switch to pass from firsttosecond position, permitting the side switch wipers 86 and 87 to engagethe contact points 95 and 96, respectively. The closure of contactbetween t e side switch wiper 87 and the contact i0 springs 161 and 162,relay 112 to the battery as lead 103, thence throu h battery B to groundG. The'release reiay 112, upon energii ing, operates 'to carry thespring 163 out efengagement with the spring 164 and into point 96 setsup an energizing circuit for the i rotary magnet 107 from ground Gthrough the interrupter spring 169, through the'winding of the rotarymagnet 107, contact point 96, side switch wiper 87 to the ,with th-i'nglG-i' This iS fl zcondition ofthe first-sel switch E 'wliefi thesubscriber operates the dial for the iii tdigit. The first digit being2, the im- "pulse spring 14 is twice carried out of engageme it with theimpulse spring 15. As

a' result the energizing circuit throughthe v linerelay 101is brokentwice, and the spring 161"comes into contact with the spring-"166 twice..After the two impulses are thus I trimsinitted,-the-line relay 101again enerand carries the spring 161 into contact with the spring 162.As previously expIained,- the relay 112 is slow-acting--that is,

" slow todeenergize; and when its energizing I: e'iifcuitis momentarilybroken, during the vertical impulses just delivered, the said does notdeenergiz'e, but remains in an opemted position with the spring 163 incontact Wlth the spring 165. Then, when his ring'lfil en'gages thespring 166, two iifip F are transmitted to the vertical In et105*iro1h-ground Gr through the sp 161*and-166 to the springs 163' and165, t rough the private magnet relay 106,

' through the windin of the vertical magnet- 105, contact int sideswitch wiper 87 v foithe battery lead 103, thence through batteryiB'to'ground G. The impulses being i r If, transmitted, the vertical magnet105' is thereby energized twice; and -the shaft :firs are? given twovertical steps in the known manner. It'will be seen that the=priiatemagnet relay-106 is included in the a energizin circuitofthevertical magnet 105.

i re

' V my also energizes but being a slow= afifing re ay it energizes-onthe first im-i pnlse -aflfllremains so until all the impulsestransmitted." This relay, upon-enerratesto close the springs 167 slid incontact, whereby sun-energizing battery lead .103, thence throughbattery B to ground G. The said rotary magnet then operates to rotatethe shaft wiper-s81, 82 and 83 of the selector E into engagement .lines,t en as soon as the private wiper 83 engages the first private bankcontact, the private magnet 88 again energizes, locking the side switchin second position. The energizing circuit for said private magnetextends from the grounded terminal G of the battery B through anoccupying switch (not shown), through the private wiper 83, thencethrough the conductor 173 to theside switch wiper 86, contact point 95,throu h the winding of theprivate magnet 88 to t e battery lead 103,thence. through battery B to ground G. The private magnet 88, upon thusbecoming energized, locks the side switch wiper 87 in, engagement withthe contact point 96, whereby the rotary magnet 107 will be energizedstep by step until the wipers are carried beyond the last busy with thefirst contact of the secondvlevelof trunk-line. At the instant that theprivate 1 wiperleaves the last busy contact point the energizing circuitthrough the .private magnet 88 is destroyed, and as a result theselector'side switch passes to third position If, however, thereare nobusy trunk lines, the private magnet '88 releases 'the side-switch tothird position as soon as the wipers are carried into engagement withthe first trunk- As soon as the side switch. passes to third position,as stated, the subscribers line conductors 19'and 20 are extended to theconductors 170 and 171, which, in this case,

s n a I.

98,. respectively.

it is assumed lead to the second-selector switch F. The extending oftheline occurs, of course, as soon as the side switch wipers 84 and 85'engage the contact points 97 and When the subscribers line conductorsare thus extended to the selector switch F an energizing circuit isestablished through the line relay 114, in the some manner in which theenergizju ing circuit was established through the line re ay 101 of theselector E when the subsoribers line conductors 19 and 20 wereextendodrtl'irough the line switch bank to the trunk conductors and 76.The relay 114, ll energizing, operates to shift the spring 41mm thespring 17 5 to the spring 176. when thesprings 174 and 176 engage, ancnergizin circuit is established through the misuse re y 124. Thiscircuit extends from as mild G through the springs 174 and 176,onfih-the relay 124 to the battery lead 103' t ence through battery B toground G.

V The relay, upon energizing, 0 rates to shift the spring 177 from thespring 17 8 to the w 4 179, and the springs 180 and 181 are n '-i' incontact. This operation of the second-selector switch F occurs at theinstant M the side switch wipers 84 and85 of the-selector switchE ass tothird position wand the subscribers line conductors l9 and 20 to thesecond-selector switch F. when the secondselector switch, therefore,thus operates, a guarding potential is establinhedat the private wiper83 for protect- T86 ing theseized trunk-line conductors 171 and 1:72againm seizure b another calling firstmlector. This guar ing potentialextends from ground G8 to the contact point 182, side switch wiper 183,through the springs 60 181 and 180, conductor 172 to the contactengtgedi'by the rivate wiper 83. Furthermore, when the rst-selector,switch E operates and the side switch passes to third position',a newenergizing circuit is established ll through therelease relay 112. Thisenergzingoircuit extends from ground G at so eetor switch F through thesprings 181 and 180, conductor 172, shaft wiper 83, condu0t0r' i173,through the side switch wiper 86, contact oint'99, relay 112, throughthe blttery' le 103, thence through battery B to ground G; The relay 112thus remains in an operated position with the spring 163 in 1' cut withthe spring 165, but the line my 101 returns to normal position when thesidoswitch wipers 84 and 85 engage the contact points 97 and 98,respective y. The" circuit through the line relay 114 extends I u 'oundG through the wind- .ing 116) to "t e side switch wiper 118,

' thence through the conductor 171, wind- 29, conductor 76 and lineconductor 20, through the primary circuit of the substation, throu thevertical line conductor 1; g")! the trunk conductor .75,

winding 21, conductor 170, side switch wiper 117, through the winding115 of the relay 114 to the battery lead 103, thence through battery Bto ground Gr. When the dial returns to normal position for the 1 seconddigit 2, this circuit through the line relay 114 is interrupted twice,when the im pulse spring 14 is carried out of engagement with the spring15 by the impulse teeth on the wheel 10. The circuit being interruptedtwice, said relay 114 momentarily deenergizes twice, thus permitting thespring 174 to engage the spring 175 a like number of times, whereby anenergizingcircuit is twice completed through the vertical magnet 120 1extending from groundGr to the springs 174 and 175, springs 177 and 179,through the winding of the private magnet relay 123, through the windingof the vertical magnet 1 20, contact point 184, side switch wiper 185 lto the battery lead 103, and through battery B to ground G. The privatemagnet relay 123 being included in this circuit energizes, and since itis a slow-acting relay it remains in an operated position until the lastver- .0 tical impulse is transmitted, and the relay 114 remainsenergized with the'spring 174 in contact with the spring 17 6, wherebythe circuit through the private magnet relay and the vertical magnet 120remains open. When the relay 123 energizes, the spnngs 186 and 187 arepressed into contact, thereby causing an energizing current to flowthrou h the private magnet 122, the circuit exten ing from ground Gthrough the springs 187 and 186, through the winding of the privatemagnet 122 to the battery lead 103, thence through battery B to groundG. When the relay 123 deenergizes and breaks the energizing circuitthrough the private magnet 122, the private magnet also deenergizes andpermits the side switch to pass from first to second position. When theside switch wiper 185 pawes to second position and finto engagement withthe contact point 188, an energizing circuit is established through therotary magnet 119, which latter now operates, as explained in connectionwith the rotary magnet 107 of the selector switch E, to select an idletrunk-line leading to the connector switch. After the switch comes torest, with the side switch in third position, the shaft wipers 189, 190and 191 are in engagement with thetrunk conductors 192, 193 and 194,respectively, which lead to the connector switch H (Fig. 2). At theinstant that the side switch wipers 117 and 118 pass to third position,in engagement with the contact points 195 and 196 the subscribers lineconductors are extended to the connectorswit'ch H and an energizingcircuit is established through the line relay 128 and the differentialrelay 23, in the same manner in which the energizing eir- .cuit wasestablished through the line relay 114 of the selector switch F when theside switch wipers of the first-selector passed :to tliirdf 'osition".'The energizing circult 6 through 't e line relay 128 extends fromground G? through the winding 130, trunk conductors 193,171 and 76 tothe line conducto'r 20, thence through the substation to the verticalline conductor 19, trunk con- .lo'ductors 7 5, 170 and 192, thencethrough the winding 129 to the battery lead 103, and ,through battery Bto ground G. The line b relay 128, upon energizing, operatesto shift thespring 196 from the spring 197 to the y 1 7 spring 198, whereby anenergizing circuit is established through the release relay 133extending from ground Gr through the .Lsprin s 196 and 198, relay 133 tothe bat- ,tery lead 103, thencethrough battery B to 0, ground G. Whenthe relay 133 energizes,

the spring 199 is shifted out of contact with the spring 200 and intocontact with the spring 201,andthe spring 202 is shifted into engagementwith the spring 203. This primary operation of the connector relays 128vand 133 occurs at the instant that the side switch wipers 117 and 118 ofthe selector F pass to third position and extend the subscribers lineconductors to the connector H. Theengagement ofthe springs 203 'and 202establishes a guarding potential for protecting the trunk-lineconductors 192 193 and 194against seizure by another line andsecond-selector. This potential extends from ground G to the side switchwiper 139, springs 203 and 202, conductor 194 to the private-bankcontact engaged by the shaft wiper 191. Furthermore, when the sideswitch of the second-selector F passes to third position a newenergizing circuit is established throu h the release relay 124, saidCircuit extenl 'ng from ground (ii at the connector switch to theconductor 194, through the shaft wiper 191, side switch 5 wiper 204,conductor-205, through the re "lease relay 124 to the battery lead 103,thence through battery B to ground GI Also, this same guarding potentialestablished at the contact enga ed-bythe private shaft wiper 191 isexten ed-to the private bank contact the shaft wiper-83 of the firsten db i gage y side switch of the secselector E, when the end-selector Fpath over whic this potential extends is as follows: from ground G 'atthe connector switch H (Fig. 2) through the side switch wiper 139,springs 203 and 202, conductor 194, shaft wiper 191, side switch wiper204,

conductor 205, contact point 206, side switch wiper 183, springs 181 and18O, cond-uctor 172 to the bankcontact engaged by the prifvate wiper 83of the selector switch E. The ,o ration of the dial for the last twodigits a ects the connector switch, and when the can is'operated for thethird digit 2 the passes to third position. The

impulse spring 14 is twice carried out of engagement with the spring 15,thereby momentarily deener izing the line relay 128 twice, whereby t espring 196 twice en-. gages the spring 197, thus sending'two impulses tothe vertical magnet 131 from ground G throu'gh the springs 196 and 197,springs 199 and 201, through the vertical magnet 131, contact point 207,side switch wiper 140, private magnet relay 134 to thebattery lead 103,thence through battery B to ground G. The private magnet relay 134energizes when the first impulse is delivered, and since the said relayis slowacting it remains'in an operated position until all the verticalimpulses are sent. The vertical magnet, upon being energized, operatesone step at a time to carry the shaft wipers 125, 126 and 127 two stepsto a-point opposite the second level. The relay134, upon energizing,shifts the spring 209 out o engagement with the spring 210 and intoengagement with the spring 211; also, the spring 212is shifted out ofengagement with the spring 211. When the springs 209 and 211 engage, anenergizing circuit is established through the; private magnet 135 fromground Gr through tht's prings 211 and 209, private magnet 135 to thebattery lead 103, thence through battery B to ground G. The relay 134,being a slow-acting-relay, remains in an operated position while thevertical impulses are being sent; but

after all the impulses are delivered, and the line relay 128 returns toits operated position, the circuit through the relay 134 becomes broken,thus permitting the springs 212 and 209 to return to normal position.When the springs 209 and 211 disengage,

the circuit through the private magnet 135 becomes broken, wherebythesaid magnet deenergizes, permitting the side switch to pass from firstto second position. The calling subscriber now operates the callingdevice for the last digit 0, thereby transmit-- ting ten impulses andoperating the line relay 128 ten times. Each time that the line relaysprings 196 and 197 engage, an energizing circuit is established throughthe rotary magnet 132 from ground G through the saidsprings 196 and 197and through the springs 199 and 201, rotary magnet 132 and locking-relaysprings 211 and 212 to side switch wiper 140, and through the privatemagnet.134 to the battery lead 103, thence through battery B to groundG. Again the private magnet relay energizes, as in the previouscase,'remai ning so until all the impulses are transmitted, therebyretaining the private magnet energized also. The rotary magnet 132 thenoperates to rotate the shaft wipers into engagement with the desiredline #2220. If this line is busyat the time, the connector side switchthe contact point 213, thence through the I mar Scription of how aconnection is established will'be' completed. As soon as the line relay128' ceases to operate for the last digit, the private magnet relay 134deenergizes, as heretofore explained, in this instance pera'mittin theside switch to trip to third position.

I e result is that the side switch wipers 136, 137, 138, 139 and 140engage the contact points 214, 215, 216, 217 and 218,v

respectively. When the side switch wiper 138engages the contact point216 a guarding potential is. completed at the private wiper 127 forprotecting the seized line from outside interference while theconnection is established. This guarding potential extends from ground Gto the contact point 216, thence by way of the side switch wiper 138,locking-relay springs 219 and 220 to the private wiper 127. Not onlydoes this arding. pOtential prevent other connectors 0m se zing the sameline. over multiples of the normal conductors 221, 222 and 223, Y but italso provides means for energizing the cut-off relay 224 of the lineswitch C, whereby the switch C is prevented from operating when thecalled subscriber removes his receiver 225 from the switch-hook 226. Itwill also be seen that when the side switch passes to third positionthetrunkrelease conductor 194 that runs between the second-selector and theconnector is provided with guarding potential from ground G through theline relay springs 196 and 198,,contact point 217, side switch wiper139, release relay springs 203 and 202 to the trunk conductor 194.However, while the side switch is in first or second position a:guarding potential for this trunk conductor 194 is also provided fromground G but through the side switch wiper 139 direct.

- the same trunk-line.

passes to third position, however, there is no such possibility, and thepotential is pro- The reason for this is that the guarding potentialfrom ground G is interrupted while the'line relay 128 is operating, andthere is some liability of some other selector similar to thesecond-selector F stopping on After the side switch I vided from groundG through the line relay springs, as stated, in order to expedite therelease of the selectors when'the calling subscriber hangs up hisreceiver Of course, when the side switch wipers 136 and 137 engage theirthird-position contact points, .214- and 215, the-calling subscribersline is placed in connection with the called subscribers line over theheavy conductors shown, passing through the ringer relay springs 227 and228 on one side, and 229 and 230 on the other side. As soon asconnection is thus established the ringer relay 145 is energized overthe circuit established when the side switch wiper 140 engages thecontact point-218, the energizing current flowing from ground G throughthe interrupter 144, through the back-ridge relay springs 231 and 232,ringer relay 145, conductor 233, contact point 218, side switch wiper140, private magnet relay 134 to the battery lead 103, thence throughbattery B to ground Gr. It will be seen that as the cuit of the ringerrelay 145 will be broken periodically, so as not to ring the calledsubscriber continuously. It will be seen that each time that the ringerrelay is energized the springs 228 and 230 are separated from the ringerrelay springs 227 and 229, thereby breaking the calling line from thecalled line and pressing the springs 228 and 23(] onto the springs 244and '245, which are the terminals of the ringer generator I. As a resultringing current is sent over the'called line for energizing the bell 234while the springs 237 and 246 are in contact. It should be explainedthat the connector H, like all the connectors. of the two-thousandtwo-hundred group, may be arranged to draw its ringing current from aringer generator I that furnishes current of such character that onlythe ringer 234 of the substation #2220 will be operated by said current;while the ringers of all other substations on the same line may be sotuned that they will not respond to the current from said generator.Similarly, the connectors of the two-thousand three-hundred group, whichare employed when substations of this group are called, may be arrangedto draw their ringing current from a rin er generator that furnishescurrent of character that only ringers tuned to respond to the currentof this particular character will be operated. Likewise, the connectorsof the four and one hundred groups of the two-thousand may in turn drawtheir ringing current from still other generators that supply current ofsuch characters that only these ringers that are correspondingly tunedwill operate. It is evident, then, that when generator current isprojected out on the line by the connector H of the two-thousand twohundred group only the ringer 234 will be operatively affected. However,as soon as the called subscriber answers, the back-bridge relay 141 isenergized by a flow of current'from ground G,

switch-hook springs. 237 and 238, impulse tssprings 339,and 240,transmitter 241, vernqnductor 221, vertical line Wiper 125, cont? tactpoint 214, side switch wiper 136, ringer relay springs 228 and 227,conductor 243,

5 winding 142 of the back-bridge relay 141, thence to the battery lead103, and through battery B to ground G. \Vhen the back- .10;- =b cidgerelay 141 is once energized, however, -the energizing circuit for theringer relay sfil45iis interrupted .at a point between the gsprings 231and 232, thus making it impos- Isiblefor theoringer relay to energize aslong calfiifasthe calledsnbscriber is on the line. The

subscribers being thus connected, they may communicate over the maintalking conilductorsindicated by the heavy lines and ina eluding on oneside the condenser 147 at the R ponnectoi' H and on the other side theconrdenaer 148. This talking circuit also in- 'cludies the windings 21and 22 of the douible-wohnd coil 23". For the purpose of l clearing thetalking circuit of the impedance W of these 'coils, theoondensers 247and 242$vv are provided across the said windings, as shown. 'Abfterthesnbscriberstre through talkingyii the calling subscriber hangs up"aihieirecetiver he opens the;line.circu-it at a 'wrpoint'hetween thesprings17 and 18, thereby i therrelease of all of, the switches.

1.1:Thisi release is as follows:' At the instant that the circuit isbroken between the said springs 17. and18,the double-wound line re-35.235133! 128and the nelease relay 1330f the connector H deene'rgize.At the instant that theisloweacting relay 133 and. the line relay 128deenergize, the energizin circuit for the areleasemagnet 133is close ata point be- ,1 other point between the springs 196 and 197. 4A.- fiow ofcurrent is, therefore, set up front ground G through. the springs 196wand 197, through the springs 199 and 200 to i the release magnet 133",thence through said magnet and to the oil-normal spring 132, .fiqto thecontact point131, and to the battery lead 103, thence through battery Bto ground G. The release magnet instantly reswitzih, therebygbreakingthe energizing cir ncuitfiirough the hack-bridge relay 141, if 1 thecalled subscriher ihas not-in the meantime restored his receiver, andalso the energizing circuitthrough the bridgecu't-ofl relay 224 ofthecalled'line switch C. As soon as the connector switch'shaft reaches;:.its,lowest positionit' breaks the circuit for the release ma et133 byseparating the ofi normal spring 132 from the contact point l3l", atwhich instant the release mag- V net ofr the connectonis also restored.The "-operr1tion of the linerelay 128 and of the :slow-acting relay -133not only causes the iez feleasegof the connector, as described, but

lease magnet 108 is closed.

tweennthe springsol99 and-200. and at anthe connector switch shaft andside.

also the release of the preceding switches,

G tothe trunk-release conductor 194 is interrupted by both of theserelays. Since the release re ays 124 and 112 are depend:

ent upon that ground for their energized the battery lead 103, thencethrough battery B to ground G. As soon as the, release magnet 121energizes, the second-selector side switch, andswitch shaft arerestored, which latter, upon reaching its lowest position, opens up therelease circuit at a point be-, tween the off-normal spring 250 and thecontact point 249, whereby the release magnet 121 is deenergized. \Vhenthe release relay 112 of the selector E deenergizes, the springs 163 and164 are brought into contact, and as a result the energizing circuit forthe re- The energizing current for this release magnet 108 then flowsfrom ground Gr through the springs 161' and 166, and through the saidsprings 163 and-164 to the release magnet 108, thence through ,saidmagnet to the contact point 'for therelease magnet 108 at a pointbetween tlie offs-normal spring 111 and contact point 110. Furthermore,when the relay 112 deenergizes and closes the springs 163 and 164 incontact, a series energizing circuit through the release magnet 24 andthe release relay 113 is established. This circuit extends from groundGr through the springs 161 and Y166, springs 163 and 164, through therelay 113, springs 251 and 252, conductor 77 to the bank springs 42 and41,

ythence through the release magnet 24 of theline switch C to the batterylead 103, ant! through battery B to ground Gr. It will be seen that therelease-magnet will then energize and, as previously explained, causethe trip armature 27 to fall over the plunger arm 22, whereby themembers 32 and 33 engage; (See Fig. 4). As the release relay 113energizes and separates the springs 251 and 252, the series releasecircuit is broken for an instant, which permits the release magnet 24 ofthe line switch C to deenergize, thereby withdrawing the plunger21because the ground-connection from ground eticalhline conductor 242,vertical normal l 1', thence to the private bank contact.

from the bank terminal Q; As a result the bank springs 41 and 42, aswell as the other bank springs of the line switch 0, are separated, thuspreventing any other action from 5- 'the trunk. After the switches arethus restored the calling subscriber can, of course,

a then proceed to make another call.

Returning now to that stage of the call where the calling subscriber wasoperating the connector switch in accordance with the *aground terminalsimilar to the ground terminal G in the connector switch H, as alreadyexplained; but if the line switch C is calling, a guarding potential isestablished from the trunk-line relay ground as in Fig. In a similarmanner the line switch 0 protects the calling line A- (when the banksprings 39and'40come into contact) from ground "G, from which groundconnection. is established through the said bank springs to the privatenormal conductor 80. Therefore, when the subscriber sends in the lastimpulse the private wiper 127 is carried onto gizes, instead of the sideswitch tripping to thirdlaausition, as in the case where the line is notsy, it is locked and the calling sub-- scriber is then given thebusy-signal. The

40 method by which this side switch is locked is as follows: Theslow-acting relay springs 209, 210 and 211 are so arranged that as therelay 134 deenergizes, the spring" 209 on gages the spring 210 before itleaves the spring 211, and in this way the private magnet 135isprevented from deenergizing, because the spring 210 is connected withthe I rivate wiper 127 at the time, over the fol spring 220, thence tothe ring 2l9 an through the winding 143 of t e back-bridge relay 141 tothe talking line conductor 235, thence through the ringer relay springs229*and'230 to the side switch wi r 137, contact point 253 (the sideswitch being in second position) to the slow-acting relay spring 210.Therefore, when the spring'209'engages the spring 210 the private magnet135 is not deenergized. since the energizing circuit is maintained fromthe rivate wiper 127 to the said spring 210,

as escribed, thence through the spring 209, and through the privatemagnet 135 to the battery lead 103, thence through battery B to groundG,- The private magnet therefore wing-:cincuit: from the private wiper127 to the l'ockin new remains energized, retaining the side switch insecond position. It will be seen that at the same time the back-bridgerelay 141 energizes in series with the privatemagnet 135, over thiscircuit, from the private wiper 127. Therefore, the back-bridge relay141, upon energizing, presses the springs 254' and 255 into contact,thereby energizing the lockingrelay 146 over the following circuit: fromground G through the slow-acting relay springs 211- and'212, through theprivate magnet springs 256 and 257, through the said relay 146, andthrough the backbridge relay springs 255'and 254' to the battery lead103, thence through-battery B'to ground G It will be seen that when therelay 146' energizes, the connection between the rotary magnet 132andthe battery lead 103 is broken at a point between the springs 211 and212-. The object of thisarrangement is to prevent the calling subscriberfrom further rotating the connector switch if he should attempt tooperate his dial while receiving the busy-signal-that is, while theconnector switch is locked in second position. It will also be seen thatwhen the relay 146 energizes, the circuitfor maintaining the privatemagnet 135 energized is shifted from theprivate wiper 127 'tothe spring258, which latter is connected to ground G. The object of thisarrangement is to prevent the side switch from unlocking and'passing tothird position, if the switch that is maintaining the called line busyshould be released while the calling subscriberA (Fig. 1) is receivingthe busy-Sig. nal. It will be evident that if the ground G were notsubstituted for the ground at the private wiper 127', the privatemagnet- 135'would deenergiz'e if the switch that is supplying ground atthe private wiper 127 should release, which would, of course, beundesirable- It will also be seen that the relay 146, uponenergizing,-closes the springs 259 and 153 in contact, therebyestablishing the busycircuit as follows: from the secondury windinoft'he busy coil 151 through the springs 15 and 259 to thesecond-position side switch contact point 260, side switch wiper 136,ringer relay springs 228 and 227, through the condenser 147, through thesubstation-A to the rotary side" of the line, then over said rotary sideback to the connector H, through the winding 180 of the line relay- 128to ground G to the interrupter ground G through the interrupter 149 tothe primary winding'of the busy coil 151 back'to the secondary winding,\Vhen the calling subscriber receives the busy-signal heunderstands'that the line is'busy and'hangs up his receiver. The linecircuit is opened, as alreadycxplained, with the result that the lineand slow acting relays 128 and 133 of theconne'ctor. H deenergize,causing the release of the connector and all other switches,

'as heretofore explained. It will, of course,

the energizin circuit for the locking relay 146' is contro led by theback-bridge relay 141, the said locking relay is also'deenerf gized, andthe connector switch is left in a...

' normal condition.

the foregoing itha's been shown how a subscriber may operate the centraloffice switches to establish connection with another line. It will nowbe pointed out how a-gisubscriber may operate the central ofliceapparatus to call and signal a party on the same line. This may be moreclearly understood'from an explanation of Fig. 3 when it is assumed thatthe subscriber at substation A desires to signal the subscriber at substation A, whose number is 5320. To call this number the substation dialis operated in theusual manner. When the line switch operates to seize atrunk-line leading to a first-xle'ctor switch, a guarding potential isestablished at the connector bank through the trupk-line relay springs,as previously explained. The master switch D operates as usual to carrythe idle plungers opposite the next available trunk-line. The impulsesfor the first digit 5 are received by thefirstselector switch E,whichoperates to select idle trunk-line leading to a second-selector F.The second-selector responds for the second digit 3 to select aconnector switch 1 H of the fi fty-three-hundred group. This connectoris operated by the last two digit impulses to select the line number 20of this roup.- The usual guarding potentials are established to protectthe various trunk lines used in establishing the connection.

As previously-explained, the trunkline relay 23 operates when theimpulses are transmitted. The operation of this relay is of noimportance until this particular timethat is, when a subscriber is aboutto operate a connector switch to callback on his own line. Thisrelay isprovided for temporarily removing the guarding potential from theconnector banks, so that the connector switch H will not find the linebusy. The operation of the trunk-line relay 23 is as follows: When theimpulses are transmitted the relay 23 deenergize's at each impulse,permitting the spring 19' to engage the spring 20 momentarily. Theengagement of these two springs provides an energizing circuit for theslow-acting relay from ground G" through the said relay, springs and19!, bank springs 40 and 39, through'the winding of the bridge-cut-offrelay 48 to the battery lead 103, thence through battery B to ground, G.The relay 15 thereupon energizes and separates the springs 16 and 17,whereb the guarding potential for the normals 0 the calling line isremoved. It will be understood, of course, that while the V relay 23energizes and deenergizes during each impulse, the slow-acting relay 15does not, since the intermittent closing of its energizing circuit issuflicient tomaintain the said relay in an operated position. After theimpulses are delivered the relay 23 remains in an energized position,maintaining bank. From the foregoing it will be seen that while impulsesare being transmitted, the protecting potential of the line iste'mporarily removed. \Vhen the connector switch is operated for thelast digit 0, the connector side switch does not lock in secondposition, but passes to third position, establishing connection with thedesired line. The subscriber at substation A having operated the centralofiice switches, including a first-selector, second-selector andconnector switch H, to call subscriber A on his own line, now pressesthe signaling button 5 in order that the ringer generator may be bridgedacross the line to signal the called subscriber. The connectors of thefiftythree-hundred group may be arranged to draw their ringing currentfrom a generator of such character that only the ringer 260 on theparty-line will be sounded, as previ-' ously explained. When thesubscriber A called the subscriber A it was explained that theback-bridge relay 141 energized when the called subscriber answered andbridged his transmitter across the line. In this instance (the calledand calling lines being identical) a provision is made where by theefl'ect of the bridgeof the calling subscribers transmitter is overcome,and the back-bridge relay 141 deenergized to permit the closing of theenergizing circuit through the ringer relay 145, as follows: When thebutton 5 is pressed the springs 6 and 7'? disengage, introducing thehigh resistance coil 8 into the circuit of the back-bridge relay 141 andthe front-bridge line relay 128. When the resistance coil 8 is placed inthis circuit sufficient current does not flow to maintain theback-bridge relay in an energized position; Hence it falls back, closingthe circuit through the ringer relay 145, as previously. However,suflicient current still flows to maintain the line relay'128 in itsenergized positionand thus prevent a premature release of the switches.lVhen the subscriber at substation A answers by removing the receiverfrom the switch-hook and bridging his transmitter across the lineconductors, a new circuit is formed which shunts the resistance coil 8.The relay 141 now ener izes, breaking the circuit of the rin er re ay145. The two substations A an A are thus placed in communication,

the guarding potential at the connector 7 vJwhich is provided with threesubstations (A, A and A) and connected to an individual or line switch]From the line switch groups trunks lead 'to first selector switches,from which latter switches trunks :lead to second selector switches.From the second selectors trunks lead to connector switches. In thisdiagram the switches and substations are represented by circles and thedifferent have s of bank contacts are represented by straight lines. Itwill be assumed that the substations A A? and A are numbered 2120, 2220,and 2320, respectively. Since the last two digits of each of thesenumbers are 20, the line to which these substations are connected wouldbe connected to the last or 0 contact in the second level in each of thethree groups of connectors H, H and H Each group of connectors isconnect ed to a dilferent generator, I, I or I, each having a differentfrequency. Since the group of connectors H is connected to the rst levelof the second selector banks, the connection with the called line willbe completed b one of these connectors if the number 21 I is called.Ringing current will then be supplied by the generator I which is of theproper frequency to actuate only the bells at substation A. It number2220 is called the connection will be completed by one of the connectorsH, and rin ing current will be furnished by generator which is of theproper frequency to signal substation A Likewise, a connection forsubstation #2320 will be completed by the connector H and ringingcurrent supplied by generator I.

From the foregoing it will be seen'that I provide efficient party-lineservice in a twowire automatic telephone exchange system that is to say,in' a system in which the Subscribers lines are free from operatinggrounds outside of the exchange or central station. It will also be seenthat I provide a two-wire automatic system .in which party-linesubscribers can signal each other on the same line through the medium ofpush-buttons at their respective stations, whereas any called subscriberwho is not on flmxsameline with the calling subscriber is automaticallysignaled from the exchange or central station. Furthermore, I provide atwo-wire automatic system in which the connectors are capable ofautomatically locking on busy lines, without closing the connection fromthe calling line to the called line, the subscriber on the calling linebeing given a busy signal. Also, and

through the medium of the slow-acting rev lays 48 and 15 and thedouble-wound line relay 23 a two-wire party-line subscriber trunkingsystem. In connection with this system it will be understood thatwhenever I use the word trunking I mean any operation that carries thecalling line nearer the called line. For example, in the connectorswitch I consider for the purposes of this application the firstoperation of the connector switch as a trunking ope-ration.

Vhat I claim as my invention is '1. In a telephone system, subscriberslines, each substation having a calling mechani'sm operative in responseto manual operation thereof to transmit current for one digit of thecalled number and then come to rest before further manual operation forthe next digit, means for extending connection to a called line by usingthe two sides of the calling line in series aplurality of substations onthe called line, means for selectively ringing the different substationson the party-line, said first means comprising a means for said trunkselector res onsive to perform the first trunking operation of theselector in response to the closure of both sides of the calling line inseries to reject busy trunks and to select an idle trunk independent ofany further action from the line.

2. In a telephone system, subscribers lines, each substation having acalling mechanism operative in response to manual operation thereof totransmit current for one digit of the called number and then come torest before further manual operation for the next digit, meansresponsive to the current corresponding to a plurality of digits of thecalled number for extending connection to a called line by using the twosides of the calling line in series, a plurality of substati'ons on thecallin line, means for releasing controlled from any calling substationon the party-line, said first means comprising a trunk selectorindividual to the calling line, trunk lines accessible to said selector,and means for said trunk selector responsive to perform the firsttrunking oeration of the selector in response to the c 'o'sure of bothsides of the calling line in series to reject busy trunks and to selectan idle trunk indeoffsubstationcontrol e'd means for ringing "anothersubstation on the same line of the called lineby using the line inseries,

calling subscriber, andautomatic means for rin g a substation on a lineother than the callhn line. a 4. l n a. telephone system, thecombination of means for extending connection to the two sides of thecallsubstation-controlled means for ringing another substation on thesame line of the calling subscriber, and automatic means for ringing asubstation on a line othertha'n the calling line. I

5.. A two wire selective ringing party-line automatic telephone exchangesystem free from operating grounds outside of the exchange or centralstation, a plurality of lines, a substation for each line, means forconnecting any two lines, sai d 'means comprising a trunk selectorindividual to the calling line, trunk lines accessible to said selector,and means for said trunk selector responsive to perform the firsttrunking operation of the selector in response to the closureofboth'sides of the calling line in series to reject busy trunks and toselect an idle trunk independent of any further action from the line,each substation having a calli ig mechanism operative in response tomanual operation thereof to transmit current for one digit of the callednumber and then come to rest before further manual operation for thenext digit;

6. A party-line automatic telephone exchange system having releasemechanism,

- and a high resistance at each substation on the party-line to preventa release when one subscriber signals another on the same line.

7. In a telephone system, a ringin key, an automatic subscribers lineprovi ed at the substation thereof with a high resistance coil normallshort-circuited by the closed contacts of t e ringing key.

"8. In a telephone s stem, a ringing key, an automatic subscri ers line,means for automatically extending connection there- ,from by using thetwo sides thereof in sefries, and a resistance'coll in the line at thesubstation thereof normally short-circuited by the closed contacts ofthe ringing key.

.9. In a telephone system, trunks for connection with calling lines,subscribers lines,

means for automatically extending connection to a called line by usingthe two sides of the calling line in series, a slow-actingbridge=cut-off relay for each line, and a double-wound relay and aslow-acting relay for each trunk to which calling lines can be i directlconnected, as set forth.

10. n a. telephone system including party lines, trunks or connectionwith callin lines, means for enabling a subscriber to call back on hisownline, comprising a slow-'acting' relay'individual to the party-line,and a slow-acting relay and another relay for each trunk to which theparty-line can be directly connected, as set forth:

substations thereon, means for automati'-' cally extending connectiontherefrom by using the two sides of the line in series, each substationhaving a caliing mechanism operative in response to manual operationthereof to transmit current for one digit of the called number and thencome to rest before further manual operation for the next digit,trunk-release circuits, means for initiating the release over the linecircuits, said first means comprising a trunk selector individual to thecalling line, trunk lines accessible to said selector and means for saidtrunk selector responsive to perform the first trunking operation of theselector in response to the closure of both sides of the calling line inseries'to reject busy trunks and to select an idle trunk independent ofany further action from the line.

12. In a'telephone system, the combination of a party-line having aplurality of substations thereon, means for automatically extendingconnection therefrom by uslng the two sides of the calling line inseries, each substation having a calling mechanism operative in responseto manual operation thereof to transmit current for one digit of thecalled number and then come to rest before further manual operation forthe next digit, trunk-release circuits provided with slow-acting releaserelays, and means for initiating the release over the line circuits.

13. A subscribers' telephone line free from operating grounds outside ofthe exchange or central station and provided with a slowactingbridge-cut-ofl' relay and a bridge-normally closed through the contactsthereof.

14. A subscribers telephone line free from operating grounds outside ofthe exchange or central station, a slow-acting bridge-cutofi' relay,abridge on said line normally closed through the contacts of said relay,a trunk, a double-wound line relay and a slowacting relay for saidtrunk, and two circuits for the first slow-acting relay, one circuitthrough the winding of the second slowacting relay and the other throughthe contacts of the same relay, both circuits controlled by said linerelay.

15. A two-wire automatic telephone exchange system free from operatinggrounds at the substations thereof provided with automatic means forlockiiig on a busy line without connecting the calling line therewith,each substation having a calling mechanism operative in response tomanual operation thereof to transmit current for one digit of the callednumber and then come

